Traditionally, splittable conjugated fiber has been used in various applications, because it forms extra fine fiber by splitting treatment.
As a conventional olefin-based splittable conjugated fiber, Publication of Examined Japanese Patent Application (Tokko) No. HEI 3-137222 (JP 3-137222 B) discloses one in which the hardness of a polymer is determined, and Publication of Unexamined Japanese Patent Application (Tokkai) No. HEI 5-321018 (JP 5-321018 A) discloses one in which a polypropylene resin is combined with a polyethylene resin blended with a polypropylene resin.
In the invention disclosed in the above-mentioned Publication of Japanese Examined Patent Application (Tokko) No. HEI 3-137222, it is described that the fiber can be split easily when the polymer itself has a hardness of not less than a certain value. However, there was a problem in that, when the polymer has a high hardness, its spinnability as well as its stretchability become poor, so that the fineness of the fiber before being split becomes large. Moreover, in the invention disclosed in the above-mentioned Publication of Unexamined Japanese Patent Application (Tokkai) No. HEI 5-321018, a polypropylene resin (a) is used as one component of the splittable conjugated fiber, and a blended resin (b) in which a polyethylene resin is blended with a polypropylene resin is used as the other component. However, when a polyethylene resin is blended with a polypropylene resin, it has an increased compatibility with the polypropylene resin (a), so that these components become difficult to split. Thus, it is necessary to increase the physical impact to split the splittable conjugated fiber. However, when the physical impact is increased, unevenness is generated in the density of the fiber existing in the obtained nonwoven fabric, so that non-uniformity is generated, and formation is deteriorated. Moreover, production of a nonwoven fabric having a low basis weight, for example, a nonwoven fabric for sanitary materials, becomes difficult. Thus, it was not satisfactory at all.